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Income Taxes (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Components of the provision for income taxes |  |
Federal | $ 0 | $ (7,439)
State | (625) | (3,842)
Deferred portion of income tax expense | (98,366) | (33,225)
Income tax expense | $ (98,991) | $ (44,506)
Effective tax rate | 23.80% | 37.40%
Tax Year 2017 [Member] |  |
Federal enacted statutory income tax rate, percent | 35.00% |
Future tax years [Member] |  |
Federal enacted statutory income tax rate, percent | 21.00% |

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